1. Vertebrate Evolution & Diversity

2. Trends in Animal Evolution
Symmetry
none  radial  bilateral
Pattern of gastrulation
no blastopore  protostome  deuterostome
Digestive system
None  gastrovascular cavity  complete digestive system
Body cavities
acoelomate  pseudocoelomate  eucoelomate
Segmentation
none  segmented  fused segments
Skeletons
none  hydrostatic  exoskeleton  endoskeleton
Is there evidence that any of these trends have reversed over time?
What are exoskeletons made of? …endoskeletons?
Consider animals with endoskeletons…Do they demonstrate evidence of segmentation? Describe the relationship.

3. Deuterostomia Phylum Echinodermata Phylum Chordata “spiny skinned”
water vascular system
What is this vascular system used for?
Phylum Chordata
named for the notochord
What features of embryonic development are shared by members of these two groups?
Do all chordates have a vertebral column?

4. Phylum Chordata (chordates) -evidence from anatomical comparisons
Segmentation: muscles arranged in segmented blocks
Most with an internal and jointed skeleton, differing from that of echinoderms 2. 1. 3. 4.
Where is the notochord located, relative to the digestive tube and nerve cord? What is its function?
Where is the nerve cord located in most non-chordate animals?
What is the pharynx? How are these slits specialized in aquatic organisms?
Describe the advantage of a muscular, post-anal tail.

5. Subphylum Urochordata – tunicates
Sessile marine animals, some are colonial
Filter-feed, using pharyngeal slits
Animal encased in a tunic of cellulose-like CHO
Larvae (c) presents all four chordate characteristics (“tail chordates”)
How have the slits been adapted for filter feeding?
Do you find evidence of segmentation in the larval form?
Fig 34.3
What is the term used to describe the change in body form here?

6. Subphylum Cephalochordata – “lancelets”
Small, burrowing animals, marine
Adults possess all four chordate traits (“head chordates”)
Suspension feeders
Muscles arranged in “chevron” (<<<<<) around notochord
Sensory tentacles around mouth
How is the mouth modified to support this method of feeding?
2 cm
Fig 34.4

7. The Origin of Vertebrates
Cephalochordates are the closest living relatives of modern vertebrates.
Larval urochordate exhibiting paedogenesis* cephalochordate ?
* Early sexual maturity. Recall that genes that control development have played a major role in evolution (pg. 478)

8. ? ancestral vertebrates, @ 530 mya
The fossil record suggests an intermediate stage between cephalochordates and vertebrates, that lacks a cranium, but has eyes.
Haikouella
Some fossils from the same period exhibit all of the vertebrate characteristics.
Myllokunmingia
? ancestral 530 mya

9. Fig 34.1
Fig 34.6
“Craniates”
Neural crest: Unique group of embryonic cells that develop into various structures, including skeletal elements like the skull.
Note that not all craniates have a vertebral column.

10. Phylogeny of Craniates
Fig 34.7
Phylogeny of Craniates
Which adaptations enabled:
better maneuvering in the environment?
more active lifestyle?
larger size?
terrestrial lifestyle?
reproduction independent of water?
Describe the blood circulatory adaptations that also support a more vigorous lifestyle.

11. Craniates
The endoskeletons of craniates are made of cartilage or a combination of cartilage and bone (mineralized tissue) How are these tissues related in embryonic development?
Hagfish
Jawless fishes
Lamprey
KEY:
yellow = fibrous c.t.
blue = bone
green = notochord
Gnathostome
“jaw”
Adapted from Tree of Life web site, available at

12. Class Myxini – hagfish All marine. Mostly bottom-dwelling scavengers
Slime glands along the sides for defense
Cartilaginous skeleton; no jaws, no teeth, no appendages, no spine
Mostly blind, well-developed sense of smell
Why are hagfishes considered the most primitive of the craniates?
Fig 34.8

13. Fig 34.1
Vertebrates
Rigid spine of cartilage or bone gives support and anchors muscles better than the notochord.

14. C. Cephalaspidomorphi – lampreys
Marine and freshwater environments
Clamp round mouth onto flank of live fish, use rasping tongue to penetrate skin and ingest blood
Cartilaginous skeleton, including spine
No paired appendages, no jaws
Fig 34.9

15. Jaws & Appendicular skeleton
Jaws and mineralized teeth: firmly grip and slice food items, eat prey that had been inaccessible
Paired appendages (fins): accurate maneuvering in aquatic environments

16. Evolution of vertebrate jaws
Fig 34.10
Evolution of vertebrate jaws
Class Chondrichthyes: sharks and rays
Gill arches evolved into jaws (and inner ear bones)

17. Lungs Lungs or lung derivatives:
in most fishes developed into swim bladder (buoyancy)
in other organisms, lungs function in
gas exchange
What are the respiratory organs in fish?

18. C. Actinopterygii - ray-finned fishes
These diverse fish have a swim bladder; it permits neutral buoyancy
Marine and freshwater environments.
-Ossified skeleton, skin often covered by flattened, bony scales.
-Skin glands secrete a mucus that reduces drag during swimming.
-Lateral line system and jaws; fins mainly supported by flexible rays.
-A protective flap called the operculum covers the gills.
-A variety of feeding mechanisms.
-Part of the “bony fishes”.
Fig 34.12a

19. Legs better locomotion in terrestrial and shallow water environments
What does “tetrapod” mean?
Does this adaptation mean a completely terrestrial lifestyle?

20. Amphibians – frogs, etc. Fig 34.17
Aquatic and terrestrial environments.
-Ossified skeleton.
-Moist skin, legs (secondarily lost in some species) and lungs (usually).
-Skin glands secrete distasteful or poisonous mucus as a protection against predators.
-Mostly carnivores.
-Frogs, toads, salamanders, and newts.
Still tied to water for reproduction, most abundant in damp habitats.
-Many go through a metamorphosis.

21. Amniotes
extraembryonic membranes (including the amnion) bring the aquatic environment onto land!
enables completion of their life cycle on land
first appeared in mammal-like reptile
Do these animals demonstrate other adaptations to life on land?

22. Amniotic egg
Fig 34.19

23. Keratinized skin; lungs; internal fertilization
“Reptiles”
Keratinized skin; lungs; internal fertilization
Fig 34.24

24. Feathers
an adaptation for thermal insulation and flight

25. Class Aves – birds Feathers
Light and hollow skeleton; - other flight adaptations
Legs and wings, most species move by flying
Amniote egg with a shell
Mouth developed into a beak
A variety of feeding mechanisms

26. Bird flight
Fig 34.26

27. Milk
provides the ability to adequately nourish offspring

28. Mammalia – mammals Hair
Mammary glands in the females to provide milk to young
Legs lost in some (marine mammals)
Amniote embryo, but does not develop a shell
Variety of feeding mechanisms

29. Which vertebrate characteristic is most responsible for their success in relatively dry environments?
Lungs and feathers were most important. That makes me best at taking advantage of the “dry” environment!
The amniote egg was the most important adaptation to life on land.
Nobody would have gotten anywhere without my cranium!
Wait a minute! I can fly…I think it’s the ability to provide milk to offspring.

30. Summary General traits of reviewed phyla, subphyla and classes
Important evolutionary trends in body plan:
Endoskeleton: Echinoderms
Notochord, nerve cord, tail, pharyngeal slits: Chordates
Cranium, brain development, neural crest cells: Craniates
Vertebral column: Vertebrates
Jaws, 2 sets of paired appendages, mineralized skeleton and teeth: Chondrichthyes (sharks and rays)
Lungs or lung-derivatives: Osteichthyes (bony fishes)
Legs: Amphibians
Amniote egg: Mammals, turtles, snakes and lizards, birds
Feathers: Birds
Milk: Mammals
These trends helped animals adapt to different environments or exploit the same environment in a different manner